The invention relates to a sensing or pick-up device for detecting pressure and temperature comprising a measuring tube and a holder of a temperature feeler.
A rather frequent task in the diagnostic determination of technical conditions of different machines, for instance of combustion engines, compressors and the like, is the determination of pressures and temperatures in the working space. Pressure pick-up devices are used for this purposed based on known piezoelectric, capacitative or tensometric principles and resistance feelers or thermoelements for picking up temperatures. If the measurements take place in a medium with a temperature above 100.degree. C., additional auxiliary cooling by a cooling medium such as water, pressure air, and the like is required for reliable, continuous operation of the pick-up device.
This usually used arrangement has a number of drawbacks from the point of view of operation. It is above all difficult under conditions of operation tests (for instance on locomotives, on tractors and the like) to employ a suitable cooling medium. The necessity to use cooling means leads to an increase of the dimensions of the device, so that it becomes impossible for most machines to situate the pick-up device as close as possible to the measured space, for instance in the cylinder of an engine. The picking-up of pressure has to be accomplished through an extending piece or fitting, which distorts the thus measured pressures. The securing and distributing of the cooling medium while simultaneous measuring pressures at a plurality of cylinders substantially complicates both the overall arrangement of the diagnostic apparatus, and also the checking of the operation of the cooling system, and thus increases the danger of failure of the device. For instance, a failure of the supply of the cooling medium in internal combustion engines causes a quick destruction of the device or sensing feeler; which is a costly part of the diagnostic arrangement.
The determination of one diagnostic value, of pressure, however, is generally not sufficient for the determination of the technical condition of a machine. It is therefore necessary to complete this reading by the determination of a further diagnostic value, the operating temperature. In case of application of customary feelers, the whole diagnostic arrangement becomes rather complicated, particularly in case of simultaneous measurements on a plurality of cylinders. For instance, for measurements on cylinders of a twelve cylinder internal combustion engine we have to provide and check the correct functioning of 24 pick-up devices (feelers) and of 12 supplies of a cooling medium, in all a total of 36 check points. Under these conditions the reliability of the measuring system frequently is lower overall than the reliability of the machine being checked.